Research On Topology And Control Strategy Of DC Bus Cascade Boost Converter System In Offshore Wind Far

With the development of wind power generation,offshore wind power generation technology has a developing trend of large-scale,large-capacity and deep-sea and far-sea.There are a series of problems in the traditional offshore centralized converter station,such as high control difficulty,high cost,high difficulty in offshore platform construction and operation and maintenance due to its complex structure,which restricts the development of offshore wind power generation.Therefore,this paper proposes a distributed power-collection and cascaded boosting-voltage system and distributed energy storage system,and focuses on its topology,operation mechanism,system control and fault tolerance,and the specific research contents are as follows:1)The topology and operation mechanism of the proposed converter system are studied.First,this paper proposes a distributed power-collection and cascaded boosting-voltage topology,which consists of multiple single active bridges(SAB)in cascade.And the SAB with cascadedconnection at secondary-side collects distributed DC energy from wind generator and deliveries to DC bus.Compared with the traditional centralized converter system,the proposed distributed cascaded boosting-voltage system has the advantages of strong boost capability,low design difficulty,low system cost,and low fault rate.Second,based on system topology analysis,system mathematical model is established and its operation mechanism is analyzed.Finally,simulation system platform is built for distributed power-collection and cascaded boosting-voltage and distributed energy storage system,and preliminary simulations and experiments are carried out,which lays theoretical and simulation foundation for the subsequent verification of system control strategies and fault tolerance strategies.2)The system control and fault tolerant control strategies are studied.First,based on system small signal model,system control strategy is designed to improve system operation stability.Second,fault tolerance strategy is proposed to deal with system faults caused by power difference,bus voltage fluctuation and branch system faults.After analyzing system operational impact caused by branch power difference,power ratio prediction and maximum power ratio adjustment strategies are proposed to improve system fault tolerance ability.Finally,simulations and experiments are carried out to verify system operational steady-state and transient performance,fault tolerance ability.And experimental results indicate that the proposed strategy improves system fault-tolerant performance by 5%.3)Power fluctuation suppression and fault tolerance strategies for distributed energy storage system are studied.First,based on distributed energy storage system mathematical model,a finite set model predictive control scheme is designed to improve energy storage system dynamic response ability.Second,power suppression and fault tolerance strategies are designed to enhance system fault tolerant ability and elasticity.Finally,simulations and experiments are carried out to verify performances of fault tolerance and power fluctuation suppression.And experimental results show that current error is reduced by 9.3% and power ratio is kept within safety limitation of 0.53.4)Experimental platform of distributed power-collection and cascaded boosting-voltage and distributed energy storage system is built.First,system main hardware circuits are designed.Second,signal acquisition and processing circuit,IGBT drive and system protection circuit are designed.Finally,the hardware experimental platform is built,which lays experimental foundation for verification of system topology and control strategy.